When I was in Douala, Cameroon for 4 1/2 months I spent a lot of time on the internet looking for good doctrine websites to inspire my teaching.
In my search, I found some outstanding websites. Here they are:
https://bookofmormon.online/home– this website was made by BYU religion professors and is the best website to look at if you want to know every detail in the Book of Mormon.
https://scriptures.byu.edu/ – this website was also made by BYU religion professors and links every scripture in the standard works to every Church talk ever recorded where that scripture was used. So one scripture can have be linked to dozens of talks. It is really useful in finding obscure conference talks and branching out to learn more doctrine and prepare for Church talks.
https://mormontextsproject.org/available-texts/ – this website has a bunch of old LDS books written by past Church leaders and authors. The books in here aren’t necessarily essential missionary readings but they are faith-promoting and interesting.
http://www.idumea.org/ – this website is entirely in French. It is made for French-speaking members and a lot of members know it including Congolese missionaries. It is a good website.
https://gospeldoctrine.com/ – this website is a good place to look at when you have questions in the scriptures. It has Church leader quotations and doctrinal commentary on nearly every scripture in the standard works.